The present invention relates to the generation of quadrature signals and more particularly to precision controlled signals for use in very high frequency wireless communication systems in the quadrature modulation and demodulation circuits thereof.
A circuit for achieving a precise fifty percent duty cycle digital signal is disclosed in which a differential ground referenced sine wave is level shifted, and then amplified and limited to provide two approximately square waves of equal amplitude but 180.degree. out of phase. The sum of the two waves is a square wave which differs from an average amplitude of zero by the error in duty cycle and used to either modulate the input sine wave or delay one of the two output signals. This circuit may use the converter.
A circuit for ensuring a 90.degree. phase differential between two signals needed for quadrature multiplication is disclosed in which the error in phase differential is filtered and amplified and used to either delay one of the two signals or to adjust the input signal.
The feedback signal from the 90.degree. phase shifter may be used to either modulate the input sine wave or delay one of the two output signals of the 50% duty cycle generator.
Unusual precision in phase control of the quadrature signals needed for modulation and demodulation of wireless signals is obtained by the use of feedback circuits in both the duty cycle generator and phase shifter.
In one aspect, the present invention achieves precision by the use of feedback loops to control both the phase differential between the quadrature signals and the generation of the 50% duty cycle signals used as input signals from which the quadrature signals are generated. The use of feedback loops for control of a 50% duty cycle generator is known (e.g., Zbinden U.S. Pat. No. 4,527,075), as is the use of feedback loops to control the phase difference between two signals (e.g., Fitzsimmons U.S. Pat. No. 5,027,124), but the combination is not. Nor is it known to use a feedback signal from the phase differential circuit to control phase shift by control of the generation of the 50% duty cycle signal generator.
In another aspect, the present invention uses the phase difference error signal as the signal which controls the operation of the 50% duty cycle generator.
Accordingly, it is an object of the present invention to provide a novel quadrature signal generator and method with multiple feedback loops and/or a feedback loop from the output all the way back to the input of the 50% duty cycle generator.
In another aspect of the present invention, it is another object of the present invention to provide a novel method and feedback circuit within the duty cycle generator.
In still another aspect of the present invention, it is an object to provide a novel method and single-ended-to-differential generator.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.